1. Field of the Invention
The present invention relates to a call destination number conversion system, and more particularly to a call destination number conversion system which offers representative phone number connection services in mobile radio communications, including cellular and cordless systems.
2. Description of the Related Art
In a mobile communications system, representative phone number connection services permit a caller to reach a member of a specific subscriber group by simply dialing the group's representative number, without the need for knowing the member's individual phone number. To make this service feature available, a representative number is previously assigned to a plurality of subscriber terminals, in addition to their own individual phone numbers in such a way that the representative number will be unique within a predivided geographical zone. When a mobile user has dialed such a representative phone number to initiate a call from a certain predivided zone, the system automatically identifies and calls up a subscriber terminal that resides in the same zone and is associated with the representative phone number that he/she dialed.
Suppose, for instance, that a certain company has a plurality of branch offices at many places in the country. More specifically, think of convenience stores operating under a franchise arrangement, or auto shops and body shops affiliated with a particular automobile manufacturer, and assume that there is a user of a mobile station who wishes to make a contact with someone in such a shop or branch office. In an attempt to call the nearest shop or office, he/she now dials a representative number of the company, without knowing the actual phone numbers of that particular shop or office. The representative phone number connection service then connects him/her to the desired place.
In such a service, a single common representative number has to be preassigned to the subscriber terminals at the branch offices, while each terminal has its own phone number. The relationships between this representative phone number and corresponding individual phone numbers are managed in a database, separately for each different geographical region. When a mobile station initiates a call by using the representative phone number, it is transferred to a mobile services switching center (MSC) via a base station. The MSC then makes access to the above database to retrieve the phone number of a subscriber terminal that is relevant to the representative phone number and location data received from the mobile station. Now that the individual phone number is obtained, the MSC sets up a connection between the mobile station and the subscriber terminal. As such, the knowledge of a common, nation-wide representative phone number permits the mobile user to call up the nearest branch office of the company, wherever he/she may be in the country.
The aforementioned database, however, tends to increase in volume, because it generally has to serve for a wide coverage area, and this results in higher equipment costs. Although this problem could be avoided by limiting the size of the database, it would impose more stringent restriction on the allowable number of subscriber terminals per representative number. In other words, it would be difficult to divide the coverage area into smaller segments to allow more subscriber terminals to share a common representative phone number. This spoils flexibility of the service.
Further, in conventional systems, the MSC has to examine each phone number received from mobile stations as to whether it is a representative phone number, and if so, the MSC has to generate a query to the database to retrieve a relevant destination phone number to which the call should be connected. This leads to a concern that such processing burden could cause degradation in the throughput and/or reliability of mobile communications systems.